Cogeneration systems offer the opportunity to reduce the cost of electrical energy for a building complex, factory, hospital, or local group, and to ensure the continuous availability of electrical energy during blackouts or xe2x80x9cbrownoutsxe2x80x9d, while simultaneously providing cooling and/or heating.
One can further improve the energy efficiency of cogeneration systems where power, heating and thermally actuated refrigeration result from the improved utilization of a single fuel source by independently controlling the simultaneous amount of each in accordance with time-varying use needs. This is a variety of xe2x80x9ccogenerationxe2x80x9d sometimes referred to as xe2x80x9ctrigenerationxe2x80x9d, to which this invention also pertains.
Many cogeneration systems and methods have been proposed in the past. Many include turbines using liquid or gaseous hydrocarbon fuels to produce electricity. Although it always is desirable to make maximum use of the fuel which is burned, it becomes even more important when the price of such fuels increases to unprecedented heights in response to artificial or naturally-caused shortages and ever-increasing demand.
Accordingly, it is an object of the present invention to provide a cogeneration system and method having improved efficiency in the usage of fuel, with maximized output of electrical energy as well as cooling and/or heating.
It also is an object of the invention to provide a cogeneration system which is relatively compact and has a relatively low initial cost.
It is a further object of the invention to provide a cogeneration system and method which are versatile in producing variable quantities of electrical power, refrigeration and heat, in accordance with varying demand.
A highly desirable cogeneration system and method are disclosed in my U.S. Pat. No. 6,050,083, and in an article entitled Cool Prescription which appeared in Consulting Specifying Engineer April, 1997. Despite the advantages of that system and method, further improvements are highly desirable, and it is an object of this invention to provide them. Certain aspects of the present system and method are set forth in the article entitled Cool Prescription, Revisited, published in Consulting Specifying Engineer, February, 2000, and the disclosure of both articles hereby is incorporated by reference.
In accordance with the present invention, the foregoing objects are met by the provision of a cogeneration system and method in which a fueled turbine is used to generate electricity and/or refrigeration, and its hot exhaust gases are used to operate one or more absorption chillers.
The hot exhaust gases preferably are used to heat a high-temperature-resistant heat transfer liquid which is connected to deliver heat to one or more absorption chillers, and to generate steam. Preferably, the heat transfer liquid flows in a closed circuit path and the absorber generator is located in the return portion of that path. The steam is used to drive a steam turbine which also generates electricity or drives mechanical refrigeration equipment.
Advantageously, in one embodiment of the invention, an absorption chiller is connected to use exhaust steam from the steam turbine as a heat source, thus increasing the refrigeration produced from the hot exhaust gases of the turbine.
In accordance with another feature of the invention, relatively low-pressure steam is extracted from the steam turbine and injected into the fueled turbine to further improve the efficiency of the fueled turbine. Advantageously, some of the steam extracted for use in deaeration of the water used in the system is the steam used for injection into the fueled turbine.
The cogeneration system and method of the present invention has numerous advantages. The invention uses energy from the fueled turbine exhaust which otherwise might be wasted. Furthermore, the fueled turbine or both turbines can be used to generate more electricity than if they also were required to drive mechanical refrigeration.
In addition, mechanical clutches to couple the turbines to the mechanical refrigeration machines are not needed because many absorption chillers do not need mechanical compression.
The use of a high-temperature resistant heat transfer liquid in the heat exchanger of the steam generator significantly reduces the size and the cost of the steam generator, and reduces its operating and maintenance costs.
In one embodiment of the invention, a second steam turbine is driven off the exhaust steam from the first steam turbine, and the shaft power of the second turbine is used to drive hybrid absorption chillers in which some mechanical compression is used.
A significant advantage of placing the generator of the absorption chiller in the heat transfer fluid return line is that this improves the efficiency of the heat exchanger in extracting heat from the fueled turbine exhaust by increasing the temperature drop across the heat exchanger, thus reducing the cost of the heat exchanger needed and improving heat recovery from the fueled turbine exhaust.
Advantageously, the temperature drop can be further increased by using the heat transfer liquid to heat hot water for use in space or process heating, and, if needed, lower-temperature hot water for distribution in a building.
An auxiliary heater can be used to heat the heat transfer liquid when the turbine exhaust is not sufficient.
Chilled water from the absorption chiller(s) can be used for space cooling, and/or to cool the inlet air temperature for the fueled turbine, and/or generate ice for storage in an ice bank.
Control of the absorptive chiller output can be obtained by use of temperature sensing and control of a bypass valve. Similar control is provided for the generation of steam and direction of the hot exhaust gases from the fueled turbine.